protection of power plants and equipment for the electrical relay against failure of high impedance.

摘要

A protective system for a polyphase distribution circuit comprises first and second ground relays 60, 60' located at a substation and a remote location respectively, each ground relay providing a time- delayed trip signal to an associated circuit breaker 52, 52' in dependence on the ratio of the zero sequence current Io to some function of the phase currents, and a zero sequence directional relay 67 at the remote location for adjusting the trip delay time of the second circuit breaker according to the flow direction of a zero sequence quantity at the remote location. IMAGE